docs: def helical_turbulent_fd_Czop (Re, Di, Dc):
      r'''Calculates Darcy friction factor for a fluid flowing inside a curved 
      pipe such as a helical coil under turbulent conditions, using the method of 
      Czop [1]_, also shown in [2]_.
          
      .. math::
          f_{curv} = 0.096De^{-0.1517}
  
      Parameters
      ----------
      Re : float
          Reynolds number with `D=Di`, [-]
      Di : float
          Inner diameter of the coil, [m]
      Dc : float
          Diameter of the helix/coil measured from the center of the tube on one
          side to the center of the tube on the other side, [m]
  
      Returns
      -------
      fd : float
          Darcy friction factor for a curved pipe [-]
  
      Notes
      -----    
      Valid for :math:`2\times10^4 < Re < 1.5\times10^{5}`. Does not use a 
      straight pipe correlation, and so will not converge on the
      straight pipe result at very low curvature.
  
      Examples
      --------
      >>> helical_turbulent_fd_Czop(1E4, 0.01, .2)
      0.02979575250574106
  
      References
      ----------
      .. [1] Czop, V., D. Barbier, and S. Dong. "Pressure Drop, Void Fraction and
         Shear Stress Measurements in an Adiabatic Two-Phase Flow in a Coiled 
         Tube." Nuclear Engineering and Design 149, no. 1 (September 1, 1994): 
         323-33. doi:10.1016/0029-5493(94)90298-4.
      .. [2] El-Genk, Mohamed S., and Timothy M. Schriener. "A Review and 
         Correlations for Convection Heat Transfer and Pressure Losses in 
         Toroidal and Helically Coiled Tubes." Heat Transfer Engineering 0, no. 0
         (June 7, 2016): 1-28. doi:10.1080/01457632.2016.1194693.
      '''
      De = Dean(Re=Re, Di=Di, D=Dc)
      return 0.096*De**-0.1517